Physics: Principles and Problems

Chapter 13: States of Matter

Problem of the Week

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Hydrostatic Pressure
What do an octopus' tentacle, an elephant's trunk, and your tongue have in common? They all make use of hydrostatic pressure to move. Most movement in your body results from muscles tugging on bones; not so for your tongue. Basic tongue motion relies upon having liquid in a chamber with muscles wrapped around it. When you put the liquid under pressure, the chamber, and consequently your tongue, will move.
When you squeeze a water balloon what happens? The part where you are not squeezing moves.

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Caecilian
Not a snake and not a worm— it is a legless amphibian. Caecilians move around in a fashion similar to your tongue. A caecilian's body cavity acts as a pressurized container. Muscles surrounding the cavity squeeze on the liquid. This increase in pressure causes the caecilian to elongate, that is, to get longer. Using this method, caecilians can produce about twice the forward force as a similar sized burrowing snake.
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To start the answer, we need to make an assumption about the muscular strength of an caecilian. Lets say that a caecilian can generate a pressure of quarter newton per square centimeter acting inward due to its circular muscles. To do the calculation, use a standard caecilian 12 cm long and 1 cm wide. Think about Pascal's principle as it applies to pistons: a force applied to one piston, the sides of the cylindrical caecilian in our case, will produce a force on a second piston, the front of the caecilian. Determine this force.

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about caecilians, see http://www.sfo.com/~morriss/eels.html#Info.
Clicking will launch a new window.
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